Rebreather - Cost of Ownership

[rjack321]

Why does a dil flush not work with an eCCR? Have I been doing it wrong?

Even if you drop your eCCR setpoint a dil flush tells you very little. Wooooeeee my dil is 1.0 on the bottom like I expected it to be. 1.0 = 1.0
I pretty much already knew that the cells would read 1.0 when I calibrated.

I want to know if 1.2 on my handset is actually 1.2 in my loop. Dil flushing doesn't confirm or deny that.

 

[doctormike]

No, but if you are doing a set point the e circuit will add O2 to maintain that value. Your flush will work, but the O2 will attempt to quickly raise your flush to the set point.

When you do a dil flush on an eCCR, you have to set your controller to low setpoint. Otherwise that happens.

 

[doctormike]

Even if you drop your eCCR setpoint a dil flush tells you very little. Wooooeeee my dil is 1.0 on the bottom like I expected it to be. 1.0 = 1.0
I pretty much already knew that the cells would read 1.0 when I calibrated.

I want to know if 1.2 on my handset is actually 1.2 in my loop. Dil flushing doesn't confirm or deny that.

Pretty sure that you know all this, but for the non-ccr divers in this thread... Those are two separate things.

If you aren't sure which of your cells is off and you suspect that the system might be voting out your one good cell, a dil flush will help confirm which one is accurately reading your dil PO2, which is the one thing that you know for sure during the dive (assuming that you know your depth). Certainly, cell response can change between calibration and the dive, due to moisture, etc...

O2 flush (on descent or ascent) detects current limitation.

So if you (1) confirm that your cells show 1.6 with an O2 flush at 20 feet (or close to it, since most O2 flushes aren't really complete), and (2) your dil flush at depth shows the expected PO2, I think that you can assume that if your handset reads 1.2 during the dive, there is 1.2 in the loop.

But I agree that ruling out current limitation should be done regularly, possibly on every dive. I was just saying that a dil flush can be useful and can be done fine on an eCCR at low setpoint.

 

[rjack321]

Pretty sure that you know all this, but for the non-ccr divers in this thread... Those are two separate things.

If you aren't sure which of your cells is off and you suspect that the system might be voting out your one good cell, a dil flush will help confirm which one is accurately reading your dil PO2, which is the one thing that you know for sure during the dive (assuming that you know your depth). Certainly, cell response can change between calibration and the dive, due to moisture, etc...

O2 flush (on descent or ascent) detects current limitation.

So if you (1) confirm that your cells show 1.6 with an O2 flush at 20 feet (or close to it, since most O2 flushes aren't really complete), and (2) your dil flush at depth shows the expected PO2, I think that you can assume that if your handset reads 1.2 during the dive, there is 1.2 in the loop.

But I agree that ruling out current limitation should be done regularly, possibly on every dive. I was just saying that a dil flush can be useful and can be done fine on an eCCR at low setpoint.

I pretty much never dil flush. It's almost useless to me. I know the cells work in the 0.7 to 1.1 range. They start the dive there (during calibration, then on the surface, potentially when I reach the bottom on descent depending on dil and depth)
There is almost no reading on my handset that makes me go "I should dil flush to see why they are reading XYZ" The one exception is a single very high cell which happened to me once a couple years ago. I did a dil flush and it was still high so I knew it was bad. But it was so widely off that really wasn't in dispute. I recall it was way over 3.0 in only 45ft of water - probably because the membrane failed.

I do add dill to bring down ppO2 - obviously. I try to spike over setpoint occasionally and I use a pressure pot periodically. dil flush? not really at all.

 

[doctormike]

There is almost no reading on my handset that makes me go "I should dil flush to see why they are reading XYZ" The one exception is a single very high cell which happened to me once a couple years ago. I did a dil flush and it was still high so I knew it was bad. But it was so widely off that really wasn't in dispute. I recall it was way over 3.0 in only 45ft of water - probably because the membrane failed.

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Right, that is exactly what I was saying. You do a dil flush when one of the cells is off and you want to make sure that that's not the good one, especially if the outlier isn't way off.

The only reason I commented in this thread was to point out that you need to go to low setpoint on an eCCR to do a dil flush. If you don't, you will never get there. When I was new I forgot to do that and ended up bailing out because I couldn't get the right PO2. I realized what I had done on the way up.

 

[bletso]

Wether you ever do a diluent flush or not, it just one of the tools available to us in our tool kit. I get the impression all of you dive ECCR. I do things a bit different. I have a DOCCR (Dual orifice CCR) One orifice supplies metabolic O2 needs and a second an add in case of exertion or a blocked orifice, (It has happened) Yes, it is a homemade unit based on the Dolphin loop. No bells, no whistles just keeping it simple and uncomplicated in the sense there is less to breakdown.

 

[tbone1004]

@rjack321 I run my setpoint around the ppO2 of my dil, so I don't dil flush to "check cells". I do however dil flush every 30 ish minutes to cool the loop down and get rid of a bunch of humidity. At least in the caves the scrubbers can start to get uncomfortably hot for me in certain rebreathers and the dil flush seems to help cool it down a little bit and get rid of some of the humidity.
Since most of my ccr diving is in 3-4ata caves with EAN32 dil, doing a dil flush can actually raise my ppO2 depending on the cave

 

[lermontov]

Right, that is exactly what I was saying. You do a dil flush when one of the cells is off and you want to make sure that that's not the good one, especially if the outlier isn't way off.

The only reason I commented in this thread was to point out that you need to go to low setpoint on an eCCR to do a dil flush. If you don't, you will never get there. When I was new I forgot to do that and ended up bailing out because I couldn't get the right PO2. I realized what I had done on the way up.

doing a dil flush must lower it though even if for a short time? am i correct in thinking your po2 was higher than your sp then? what was it? im assuming you BO because the PO2 of the wayward cell wasnt responding?

 

[doctormike]

doing a dil flush must lower it though even if for a short time? am i correct in thinking your po2 was higher than your sp then? what was it? im assuming you BO because the PO2 of the wayward cell wasnt responding?

It lowers it intermittently and inconsistently, because you are bleeding dil into the loop at the same time that the solenoid is bleeding O2 into the loop. At points it can actually spike if the cells are exposed to a high O2 stream - since you have these two streams of gas going into the loop at the same time, you really don't get homogenization and you get widely varying PO2 on each cell surface. With a proper dil flush, you get a nice solid reading at dil PO2 which holds after the flush. In my case, I got the former rather than the latter, knew that was a problem, and since I didn't at that time realize what the problem was, I opted to bail out.

As for the specifics - dive to 4 ATA with air dil. Dil PO2 at depth=0.84, setpoint 1.3.